This report provides the first comprehensive study of publicly capitalized green investment banks, analyzing the rationales, mandates, and financing activities of this relatively new category of public financial institution. Based on the experience of over a dozen green investment banks and similar entities, the report provides a nonprescriptive stocktaking of the diverse ways in which these public institutions are catalyzing private investment in low carbon, climate resilient infrastructure and other green sectors, with a spotlight on energy efficiency projects. The report also provides practical information to policymakers on how green investment banks are being set up, capitalized, and staffed.